do-release-upgrade fails: TypeError: decode() argument 1 must be string, not None

[Christian Weiske]

Trying to upgrade from 12.04 to the next version, I get the following error:

$ LC_ALL=C do-release-upgrade
....
WARNING: Failed to read mirror file

Third party sources disabled

Some third party entries in your sources.list were disabled. You can
re-enable them after the upgrade with the 'software-properties' tool
or your package manager.

To continue please press [ENTER]

A fatal error occurred

Please report this as a bug and include the files
/var/log/dist-upgrade/main.log and /var/log/dist-upgrade/apt.log in
your report. The upgrade has aborted.
Your original sources.list was saved in
/etc/apt/sources.list.distUpgrade.

Traceback (most recent call last):

File "/tmp/update-manager-ewoDWd/quantal", line 10, in <module>
sys.exit(main())

File "/tmp/update-manager-ewoDWd/DistUpgrade/DistUpgradeMain.py",
line 240, in main
if app.run():

File
"/tmp/update-manager-ewoDWd/DistUpgrade/DistUpgradeController.py",
line 1764, in run
return self.fullUpgrade()

File
"/tmp/update-manager-ewoDWd/DistUpgrade/DistUpgradeController.py",
line 1663, in fullUpgrade
if not self.updateSourcesList():

File
"/tmp/update-manager-ewoDWd/DistUpgrade/DistUpgradeController.py",
line 803, in updateSourcesList
_("Some third party entries in your sources.list "

File "/tmp/update-manager-ewoDWd/DistUpgrade/DistUpgradeViewText.py",
line 138, in information
sys.stdin.readline().decode(ENCODING, "backslashreplace")

TypeError: decode() argument 1 must be string, not None

[Christian Weiske (cweiske)]

The error does not happen if I remove LC_ALL=C and did
$ apt-get install language-pack-en-base
$ dpkg-reconfigure locales

I nevertheless think that the bug should be fixed, since LC_ALL=C is the standard way to get english messages on an non-english system.